The invention relates broadly to color digital-graphics projection displays based on primary color digital-graphic-encoding beam modulator panels and projection optics for such projection displays. More particularly, the invention relates to such color digital graphics projection displays and projection optics providing compensation for a lateral color chromatic aberration.
A typical color digital-graphics projection display arrangement uses three digital-graphic-encoding beam modulator panels, one for each of a red, a green, and a blue component of a color graphic. Examples of beam modulator panels include transmissive polysilicon liquid crystal displays (LCDs), reflective digital micromirror devices (DMDs), and reflective liquid crystal displays (RLCDs)xe2x80x94also known as reflective liquid crystal on silicon displays (LCoS). Often graphic-encoded beams from the three panels are combined optically with component-color beam recombination optics and projected through a single projection lens.
With increasing demands for higher resolution, higher pixel count, and smaller devices, the difficulty of designing projection lenses for color digital-graphic projection displays has increased. One characteristic of a projection lens that becomes emphasized is a characteristic referred to as xe2x80x9clateral color.xe2x80x9d Lateral color refers to a chromatic aberration involving a dependence in lateral magnification of a graphic on the wavelength or color or color of the graphic. Such a change in lateral magnification with color typically results in a change in the convergence of the superimposed component-color imaged graphics from red, green, and blue digital-graphic encoding beam-modulator panels from the center of a projected graphic display outwards. So, if digital-graphic-encoding panels are positioned so that there is perfect convergence of the component color pixels of a graphic in the center of the display, the color convergence can be off by a pixel or more at the edge of the display. Such variation in color convergence degrades graphic quality, particularly for projection of computer graphics displays.
Limiting lateral-color misconvergence is a significant issue in the development of three-panel projection monitors. For example, a projection monitor employing panel arrays having 1200xc3x971600 pixels, with each pixel being about 10 microns square, and subject to a design objective of a half pixel or less of lateral-color misconvergence presents a difficult objective for a projection lens maker to achieve. A conventional projection monitor with such panel arrays might have a lateral-color misconvergence at the corners of the graphic of about 12 microns measured at the panel arrays, which is greater than a pixel. Lateral-color misconvergence of such magnitude is a significant problem in computer display monitor applications, where icons and menus are typically placed at the edges of the graphic display. In general, to compensate for lateral color effects, a projection lens would have to increase in size and contain additional elements, which results in an increase in design complexity and cost. As a practical matter, lens design alone is not enough to meet the demands of increased display resolution.
An emerging direction in electronic projection displays is reflective-polarization-modulator based systems employing reflective liquid-crystal polarization modulators. Many of the architectures based on reflective polarization modulators employ arrangements where the distance from the polarization-modulator panel to the projection lens is large compared to the focal length of the projection lens. This is especially true for rear projection displays, such as projection monitors and projection television. In general, the greater the back-focal distance, the more difficult it is to produce a projection lens. Another optical design constraint that makes a projection lens a challenge to produce for such systems is a requirement for xe2x80x9ctelecentricity.xe2x80x9d A telecentric lens system has an entrance pupil at infinity. In terms of chief raysxe2x80x94also termed xe2x80x9cprincipal raysxe2x80x9dxe2x80x94having an entrance pupil at infinity means that the chief rays are parallel to the optical axis, thus resulting in every point on an image possessing the same set of angles or pupil properties.
A conventional digital-graphic projector employing reflective liquid-crystal polarization modulators and a telecentric projection lens is disclosed in U.S. Pat. No. 5,777,789 to Chiu et al. The projector of the ""789 patent has a metal-halide arc lamp as a source of unpolarized xe2x80x9cwhitexe2x80x9d light for the projector. Light from the arc lamp passes through illumination optics which function to form a generally parallel, visible white-light illumination beam of generally uniform intensity spatially with respect to polarization-modulator faces of the liquid-crystal polarization modulators employed in the projector. The unpolarized illumination beam is directed into a polarizing beamsplitter cube, which splits the unpolarized beam into two beams of substantiallyxe2x80x94but, conventionally, not perfectlyxe2x80x94polarized light, with the respective polarizations of the two beams being substantially orthogonal. One of the two light beams so produced in the polarizing beamsplitter cube of the digital-image projector of the ""789 patent serves as a substantially polarized source beam and is directed from the splitting/combining prism assembly is comprised of three prisms with certain of the faces of the prisms bearing dichroic coatings for sequentially separating red, blue, and green light components from the visible white light of the substantially polarized source beam and directing each substantially polarized component-color light beam onto a corresponding reflective liquid-crystal polarization modulatorxe2x80x94referred to as a xe2x80x9clight valvexe2x80x9d in the ""789 patent.
Each of the three polarization modulators of the digital-image projector of the ""789 patent is positioned with a reflective polarization-modulator face perpendicular to a component-beam optical path defined with respect to the corresponding substantially polarized color-component light beam exiting a color-component output face of the color splitting/combining prism assembly. According to the ""789 patent, the images of the reflective liquid-crystal polarization modulators are brought into coincidence upon the projection screen by mechanical adjustment of the polarization modulators relative to the color-component output faces of the prism assembly. In general, a reflective polarization modulator serves to modulate the polarization of the corresponding color-component light beam spatially by means of selective rotation of the polarization of the light of the beam on a pixel-by-pixel basis over the polarization-modulator face in accordance with a signal applied to the polarization modulator which encodes a component color image of a desired composite color graphic. In particular, for each pixel of the final imaged graphic which is to be illuminated in a given color, the polarization of the substantially polarized color-component light beam of that color is rotated by the reflective liquid-crystal polarization modulator at a location on the polarization-modulator face corresponding to the location of the pixel in the final imaged graphic. Such illuminated pixels are referred to as xe2x80x9clightxe2x80x9d pixels. Conversely, for each pixel of the final imaged graphic which is not to be illuminated in a given color, the substantially polarized color-component light beam of that color is reflected with the polarization of the beam unchanged by the reflective liquid-crystal polarization modulator at the location on the polarization-modulator face corresponding to the location of the pixel in the final image graphic. Such non-illuminated pixels are referred to as xe2x80x9cdarkxe2x80x9d pixels.
The color-component light beam thus spatially selectively polarization modulated by a liquid-crystal polarization modulator of the digital-graphics projector of the ""789 patent is reflected from the reflective polarization-modulator face of the polarization modulator substantially back along the corresponding component-beam optical path through the color splitting/combining prism assembly. Each of the three reflected color component light beams substantially retraces its original path through the prism assembly and recombines with the other two color component light beams to form one composite spatially selectively polarization-modulated light beam. The composite light beam emerges from the color splitting/combining prism assembly and passes into the polarizing beamsplitter cube. The polarizing beamsplitter cube splits the composite light beam into a polarization-modulated light-pixel component beam which carries the composite color graphic made up of light pixels and a non-polarization-modulated dark-pixel component beam which carries a color-negative graphic made up of dark pixels. Since the polarization of the dark-pixel component beam was unchanged by the reflective liquid-crystal modulators, the dark-pixel component beam retraces an optical path through the projector back towards the arc lamp which was the source of illumination. The polarization-modulated light-pixel component beam is directed from the polarizing beam splitter into a projection lens of the digital-graphics projector of the ""789 patent. According to the ""789 patent, the projection lens is a retrofocus telecentric lens designed to accommodate a large glass working distance and telecentric illumination. The projection lens serves to project the desired composite color graphic onto a projection screen.
In general, designers of projection displays strive to achieve a xe2x80x9cperfectxe2x80x9d projected graphic. However, projection-display designers are faced with difficulties such as maintaining proper image height in the projected graphic and lateral color effects, to name a few. With either a single digital-graphic-encoding beam modulator panel or multiple beam modulator panels and a telecentric system, a designer must achieve such a xe2x80x9cperfect imaged graphicsxe2x80x9d through lenses. However, to achieve a xe2x80x9cperfectxe2x80x9d imaged graphic through lens systems alone is problematic and frequently so costly as to be beyond economic feasibility. Whether such lens systems are situated in front of or behind a beam modulator panel, there are often problems with lateral color, even with the best lens systems currently available. A projection-display designer who is trying to achieve a xe2x80x9cperfectxe2x80x9d imaged graphic is constrained as a practical matter by lens systems.
What is needed is a projection display system that provides compensation for lateral color effects, and which simplifies lens design so that satisfactory color convergence can be achieved over an entire projected graphic. An advance in the art is achieved with a projection-optics lens assembly and digital graphics projection display of the invention providing excellent compensation for lateral color effects for digital color-graphics projection.
Broadly, compensation of lateral-color chromatic-aberration effects in a digital color-graphics projection display is achieved in the invention by providing projection optics for the projection display which is nontelecentric to a certain degree to establish an angled geometry for gathering light off axis for projection by the projection optics and by providing object planes for object digital graphics of different primary colors to be projectively displayed through the projection optics which are located at different effective axial distances from the projection optics, which axial distances are respectively keyed to the angled geometry of the off-axis light gathering of the projection optics and to lateral-color chromatic-aberration differences in lateral magnification by the projection optics at different primary colors so that such color-dependent differences in lateral magnification tend to be compensated.
Preferably, the projection optics of a digital color-graphics projection display of the invention provide three component-primary-color object planes respectively for object graphics of red, green, and blue. The effective axial distances of the three component-primary-color object planes from the projection optics preferably differ from one another.
The projection display of the invention preferably includes three component-primary-color digital-graphic-encoding beam-modulator panels corresponding respectively to one of the component primary colors of red, green, and blue. Each beam-modulator panel preferably comprises a plurality of optical-modulator pixel elements arranged in a planar array. Each of the component-primary-color digital-graphic-encoding beam-modulator panels is preferably positioned with the planar array of optical-modulator pixel elements of the beam-modulator panel located proximate to the corresponding component-primary-color object plane of the projection display. Each optical-modulator pixel element of a component-primary-color beam-modulator panel is adapted to controllably modulate optically light illuminating the pixel element in accordance with graphics-encoding control signals applied to the beam-modulator panel. The optical-modulator pixel elements of a component-primary-color beam-modulator panel are preferably adapted collectively to spatially optically modulate on a pixel array basis a component-primary-color light beam illuminating the beam-modulator panel in accordance with a corresponding primary-color graphic component of the desired composite-color digital graphic to form a graphics-encoded component-primary-color beam. A component-primary-color encoded-beam central axis may be defined respectively for each graphics-encoded component-primary-color beam with each component-primary-color encoded-beam central axis intersecting the corresponding component-primary-color beam-modulator panel at essentially normal incidence at a component-primary-color modulator-panel central-axis intersection point. Respective planar arrays locating the positions of optical-modulator pixel elements on the three component-primary-color beam-modulator panels together with the respective component-primary-color modulator-panel central-axis intersection points are preferably essentially geometrically congruent with one another. An object pixel-spacing distance may be defined as an average center-to-center distance between adjacent pixel elements in the beam-modulator panels.
The composite-color image plane of the projection display of the invention preferably has an array of composite-color pixel locations defined with respect thereto. Each composite-color pixel location in the composite-color image plane preferably corresponds to three optical-modulator pixel elements located respectively at essentially congruent positions on the beam-modulator panels. A projection-optics central axis may be defined with respect to the projection optics passing centrally through the projection optics. The projection optics of the projection display of the invention has a projection optics aperture stop located at a projection-optics aperture stop location along the projection-optics central axis. A composite-color image-plane central-axis intersection point may be defined by an intersection of the projection-optics central axis with the composite-color image plane corresponding to the three component-primary-color modulator-panel central-axis intersection points.
A composite-color image test-point location is preferably defined in the composite-color image plane of the projection display of the invention laterally displaced from the composite-color image-plane central-axis intersection point and corresponding to a location of a single composite-color pixel in the composite-color image plane. The composite-color image test-point location in the composite-color image plane preferably corresponds to three optical-modulator object test-point pixel elements located respectively at essentially congruent positions on the three component-primary-color beam-modulator panels. For each component primary color, a component-primary-color test-point chief ray trace may be defined, tracing as a ray of light of the component primary color, from the composite-color image test-point location in the composite-color image plane through the projection optics, passing through a center point of the projection-optics aperture stop, and through any intervening optics of the projection display to intersect the corresponding component-primary-color beam-modulator panel at a point laterally displaced from the central-axis intersection point of the beam-modulator panel. Each of the three component-primary-color test-point chief ray traces optically traces a component-primary-color-dependent path manifesting chromatic aberrations of the optics through which the chief ray trace passes including the lateral-color chromatic-aberration differences in lateral magnification. The projection-optics aperture-stop location of the projection-optics aperture stop of the projection optics of the projection display of the invention is a nontelecentric aperture-stop location such that each component-primary-color test-point chief ray trace intersects the corresponding component-primary-color beam-modulator panel at a nontelecentric angle of intersection inclined with respect to a normal to the beam-modulator panel at the point of intersection in accordance with the angled geometry for gathering light off axis for projection by the nontelecentric projection optics. Each of the three component-primary-color beam-modulator is preferably individually positioned axially with effective axial distances from the projection optics so that, taking into account the nontelecentric angle of intersection of the component-primary-color test-point chief ray trace with the corresponding component-primary-colors beam-modulator panel and chromatic aberrations including the lateral-color chromatic-aberration differences in lateral magnification at the respective component primary colors, the corresponding component-primary-color test-point chief ray trace intersects the beam-modulator panel within about one half of the pixel-spacing distance of a center of the corresponding object test-point pixel element, so that differences in the lateral magnification of light rays of different component primary colors of the projection optics tend to be compensated for over the composite-color graphics imaged by the projection optics in the composite-color image plane.
The digital-graphic-encoding beam-modulator panels of the projection display of the invention may include transmissive polysilicon liquid crystal displays (LCDs), reflective digital micromirror devices (DMDs), or reflective liquid crystal displays (RLCDs).
In one embodiment of the projection display of the invention, each of the component-primary-color digital-graphic-encoding beam-modulator panels is positioned with the planar array of optical-modulator pixel elements of the beam-modulator panel located essentially coincident with the corresponding component-primary-color object plane. In an alternative embodiment of the projection display of the invention, at least one of the component-primary-color digital-graphic-encoding beam-modulator panels is positioned with the planar array of optical-modulator pixel elements of the beam-modulator panel spaced apart from the corresponding component-primary-color object plane by a component-primary-color pixel convergence defocus distance so that the corresponding component-primary-color test-point chief ray trace intersects the beam-modulator panel within about one half of the object pixel-spacing distance of the center of the corresponding optical-modulator object test-point pixel element.
A projection-optics lens assembly of the invention for a digital-graphics color projection display which permits lateral-color chromatic-aberration effects to be effectively compensated has a projection-optics entrance optical port and a projection-optics exit optical port. A projection-optics central axis is defined with respect to the projection-optics lens assembly passing centrally through the lens assembly and extending axially from the entrance optical port and the exit optical port.
A composite-color-graphics projection-display image plane in which composite-color graphics may be imaged by the projection-optics lens assembly of the invention is defined with respect to the lens assembly to extend substantially normally to the projection-optics central axis of the lens assembly spaced apart in a projected-beam exit propagation direction from the projection-optics exit optical port. An image-plane central-axis intersection point in the composite-color-graphics projection-display image plane is defined by an intersection of the projection-optics central axis with the image plane.
For each of three component primary colorsxe2x80x94preferably; red, green, and bluexe2x80x94a component-primary-color projection-display object plane is defined to extend substantially normally to the projection-optics central axis of the projection-optics lens assembly of the invention spaced apart in a direction opposing a projected-beam entrance propagation direction from the projection-optics entrance optical port. A component-primary-color object-plane central-axis intersection point is defined respectively for each of the three component-primary-color projection-display object planes by an intersection of the projection-optics central axis with the respective object plane.
For each of the three component primary colors, the projection-optics lens assembly of the invention is adapted to projectively image a graphic of the component primary color located in the corresponding component-primary-color projection-display object plane onto the composite-color-graphics projection-display image plane. The projection-optics lens assembly exhibits a lateral-color chromatic aberration. For example, lateral magnification of a test composite-color object graphic having lateral extent relative to the projection-optics central axis placed at a test object location along the projection-optics central axis and projected by the lens assembly onto the composite-color-graphics projection-display image plane would differ for different component primary colors.
The projection-optics lens assembly of the invention includes an entrance optical element having an entrance optical surface located at the projection-optics entrance optical port. An intersection of the projection-optics central axis and the entrance optical surface of the projection-optics lens assembly defines an object-plane distance base point. A component-primary-color object-plane axial-position distance is defined respectively for each component-primary-color projection-display object plane measured from the object-plane distance base point on the entrance optical surface of the projection-optics lens assembly to the object-plane central-axis intersection point of the respective component-primary-color object plane.
The projection-optics lens assembly of the invention has a projection-optics aperture stop located at a projection-optics aperture-stop location along the projection-optics central axis.
A composite-color image test-point location with respect to the projection-optics lens assembly of the invention is defined in the composite-color-graphics projection-display image plane laterally displaced from the image-plane central-axis intersection point. For each component primary color, a component-primary-color test-point chief ray trace is respectively defined, optically tracing as a ray of light of the respective component primary color, from the laterally displaced composite-color image test-point location in the composite-color-graphics projection-display image plane into the projection-optics exit optical port, through the projection-optics lens assembly passing through a center point of the projection-optics aperture stop, and out of the projection-optics entrance optical port to intersect the corresponding component-primary-color projection-display object plane. Each of the three component-primary-color test-point chief ray traces respectively traces a corresponding component-primary-color-dependent path through the projection-optics lens assembly manifesting chromatic aberrations of the lens assembly, including the lateral-color chromatic aberration. A point of intersection between each component-primary-color test-point chief ray trace and the corresponding component-primary-color projection-display object plane defines a corresponding component-primary-color object test-point location. Each of the three component-primary-color object test-point locations is optically conjugate for light of the corresponding component primary color to the laterally displaced composite-color image test-point location in the composite-color-graphics projection-display image plane. Each component-primary-color object test-point location is laterally displaced from the object-plane central-axis intersection point of the corresponding component-primary-color projection-display object plane to define a component-primary-color object-test-point lateral-displacement distance.
The projection-optics aperture-stop location of the projection-optics aperture stop of the projection-optics lens assembly of the invention is a nontelecentric aperture-stop location. As a consequence of the nontelecentric aperture-stop location, each component-primary-color test-point chief ray trace intersects the corresponding component-primary-color projection-display object plane at a nontelecentric angle of intersection inclined with respect to a normal to the object plane at the point of intersection. The three component-primary-color projection-display object planes have respective axial positions along the projection-optics central axis such that, taking into account the nontelecentric angle of intersection of the corresponding component-primary-color test-point chief ray trace with the respective component-primary-color object plane and chromatic aberrations including the lateral-color chromatic-aberration differences in lateral magnification of the lens assembly at different component primary colors, the component-primary-color object-test-point lateral-displacement distances for the three component-primary-color projection-display object planes are essentially equal to one another. The respective axial positions of the three component-primary-color projection-display object planes are such that the respective component-primary-color object-plane axial-position distances of at least two of the three component-primary-color projection-display object planesxe2x80x94and preferably all three of the component-primary-color object planesxe2x80x94differ from one another so that differences in the lateral magnification of light rays of different component primary colors caused by the lateral-color chromatic aberration of the projection-optics lens assembly of the invention tend to be at least partially compensated for over the composite-color graphics imaged by the lens assembly in the composite-color-graphics projection-display image plane.
Preferably, the projection-optics lens assembly of the invention is adapted to projectively image object graphics of each of the three component primary colors which are dimensioned to fit within a corresponding generally rectangular object-graphic field referenced to the corresponding component-primary-color projection-display object plane. Such an object-graphic field preferably corresponds to the dimensions of a modulator face of a digital-graphic-encoding beam modulator panel, for example. Each of the object-graphic fields has a height dimension which is the same for all three object-graphic fields and a width dimension which is the same for all three object-graphic fields. Each object-plane axial-position distance between the object-plane distance base point on the entrance optical surface of the projection-optics lens assembly and the object-plane central-axis intersection point of the corresponding component-primary-color object plane is preferably at least twice the value of the lesser of the height dimension and the width dimension of the object-graphic fields so that when such projection-optics lens assembly is incorporated in a digital-graphics projection display, polarizing-beamsplitter elements and beam color dividing/combining elements may be accommodated between the projection-optics entrance port of the lens assembly and component-primary-color digital-graphic-encoding beam modulator panels of the projection display, which preferably are respectively located an effective axial distance from the projection optics entrance port equal to the corresponding component primary-color object-plane axial-position distance.
An image-graphic field is preferably defined on the composite-color-graphics projection-display image plane for a projection-optics lens assembly of the invention to correspond to an image of object-graphic fields of the component-primary-color projection-display object planes. Preferably, the composite-color image test-point location on the composite-color-graphics projection-display image plane is located within the image-graphic field proximate to a perimeter of the image-graphic field.
Preferably, in projection-optics lens assemblies of the invention, each component-primary-color test-point chief ray trace at the point of intersection with the corresponding component-primary-color projection-display object plane tracing in a direction generally opposing a projected-beam entrance propagation direction diverges from the projection-optics central axis.
Preferably, the respective component-primary-color object-plane axial-position distances of the three component-primary-color projection-display object planes differ from one another in a projection-optics lens assembly of the invention.
A projection display of the invention for projecting a desired composite-color digital graphic for viewing preferably includes a projection display housing and an illumination source positioned within the projection display housing at an illumination-source object location for providing white-spectrum illumination light. Preferably, beam-forming optics are positioned within the projection display housing to receive illumination light from the illumination source. The beam-forming optics are adapted to form from such light a focused illumination beam propagating substantially along an illumination-beam central axis defined with respect to the beam-forming optics.
The projection display of the invention preferably also includes a polarizing beamsplitter. An illumination-beam-reception axis, a dark-pixel-polarization-state polarized beam axis, and a light-pixel-polarization-state polarized beam axis are defined with respect to the polarizing beamsplitter. The polarizing beamsplitter is adapted to receive an illumination beam propagating towards the polarizing beamsplitter substantially along the illumination-beam reception axis, to divide from the illumination beam a linearly polarized dark-pixel-polarization-state beam propagating outwardly from the polarizing beamsplitter substantially along the dark-pixel-polarization-state polarized beam axis, to receive a mixed-polarization graphics-encoded beam containing dark-pixel-polarization-state linearly polarized light bearing a color-negative graphic and light-pixel-polarization-state linearly polarized light bearing a desired composite-color graphic propagating towards the beamsplitter substantially along the dark-pixel-polarization-state polarized beam axis, and to divide the mixed-polarization graphics-encoded beam into a dark-pixel-polarization-state linearly polarized beam bearing the color-negative graphic propagating away from the polarizing beamsplitter substantially along the illumination-beam-reception axis and a light-pixel-polarization-state linearly polarized beam bearing the desired composite-color graphic propagating outwardly from the polarizing beamsplitter substantially along the light-pixel-polarization-state polarized beam axis. The illumination-beam reception axis of the polarizing beamsplitter is preferably effectively aligned with the illumination-beam central axis of the illumination-beam forming optics.
The projection display of the invention preferably further includes beam color dividing/combining optics having a composite beam input/output optical port and three component-primary-color subbeam output/input optical ports. The beam color dividing/combining optics is adapted to accept a white-spectrum input beam propagating substantially along a composite-beam input/output central axis into the composite beam input/output optical port, divide the white-spectrum input beam into three component-primary-color output subbeams, and project each of the component-primary-color output subbeams respectively from the corresponding component-primary-color output/input optical port propagating substantially along a corresponding component-primary-color subbeam output/input central axis. The beam color dividing/combining optics is further adapted to accept respectively input subbeams of each of the three component primary colors propagating substantially along the corresponding component-primary-color subbeam output/input central axis into the corresponding one of the three component-primary-color output/input optical ports, combine the three component-primary-color input subbeams into a composite-color output beam, and project the composite-color output beam from the composite beam input/output optical port propagating substantially along the composite-beam input/output central axis. Preferably, the beam color dividing/combining optics are positioned and oriented in the projection display housing with the composite-beam input/output central axis in effective alignment with the dark-pixel-polarization-state polarized beam axis of the polarizing beamsplitter. Preferably, corresponding to each component primary color, a component-primary-color central optical path is defined passing through the beam color dividing/combining optics and the polarizing beamsplitter as a central axis of a light-pixel-polarization-state linearly polarized subbeam of light of the corresponding component primary color propagating into the corresponding component-primary-color subbeam output/input optical port substantially along the corresponding component-primary-color subbeam output/input central axis through, in turn, the beam color dividing/combining optics and the polarizing beamsplitter and outwardly from the polarizing beamsplitter substantially along the light-pixel-polarization-state polarized beam axis.
The projection display of the invention preferably also comprises projection optics mounted to the projection display housing having a projection-optics entrance optical port and a projection-optics exit optical port. A projection-optics central axis is preferably defined with respect to the projection optics passing centrally through the entrance optical port and the exit optical port. Preferably, the light-pixel-polarization-state polarized beam axis of the polarizing beamsplitter is effectively aligned with the projection-optics central axis of the projection optics. The projection optics has a projection-optics aperture stop located at a projection-optics aperture-stop location along the projection-optics central axis. The projection optics is adapted to receive through the entrance optical port a composite-color graphic-bearing beam propagating substantially along the projection-optics central axis and project the beam through the exit optical port to effectively image the composite-color graphic in a graphics display image plane which preferably extends substantially normally to the projection-optics central axis. The projection optics preferably includes an entrance optical element having an entrance optical surface through which passes the graphic-bearing beam entering the entrance optical port. Preferably, a projection-object-distance base point is defined as an intersection of the projection-optics central axis and the entrance optical surface of the projection optics. The projection optics exhibits a lateral-color chromatic aberration. For example, lateral magnification of a test composite-color object graphic having lateral extent relative to the projection-optics central axis placed at a test object graphic location along the projection-optics central axis and projected by the projection optics onto the graphics display image plane would differ for different component primary colors.
Preferably, the projection display of the invention further comprises three reflective component-primary-color digital-graphic-encoding polarization modulators. Each reflective component-primary-color polarization modulator preferably has a substantially planar reflective polarization-modulator face comprising a plurality of individually controllable reflective polarization-modulator pixel elements arranged in a planar array. Each such reflective component-primary-color polarization modulator is preferably positioned in an output subbeam interception relationship with a corresponding one of the three component-primary-color output/input optical ports of the beam color dividing/combining optics and preferably oriented with the polarization-modulator face of the reflective polarization modulator facing the corresponding component-primary-color output/input optical port and extending substantially normally to the corresponding component-primary-color subbeam output/input central axis. Preferably, a polarization-modulator-face central-axis intersection point is defined for each reflective polarization-modulator face as a point of intersection of the polarization-modulator face with the corresponding component-primary-color subbeam output/input central axis. Preferably, respective planar arrays locating the positions of reflective polarization-modulator pixel elements on the polarization-modulator faces of the three component-primary-color polarization modulators together with the respective polarization-modulator-face central-axis intersection point of the polarization-modulator faces are essentially geometrically congruent with one another. A polarization-modulator-face axial-position distance is preferably defined for each reflective polarization-modulator face measured from the polarization-modulator-face central-axis intersection point of the polarization-modulator face to the projection-object-distance base point on the entrance optical surface of the projection optics along the corresponding component-primary-color central optical path passing through the beam color dividing/combining optics and the polarizing beamsplitter.
Preferably, each reflective polarization-modulator pixel element in a reflective component-primary-color digital-graphic-encoding polarization modulator of a projection display of the invention is adapted to reflect linearly polarized component-primary-color light falling upon the pixel element and to modulate the polarization of the reflected linearly polarized light in accordance with graphics encoding control signals applied to the polarization modulator. Preferably, the reflective polarization-modulator pixel elements of a polarization-modulator face of a component-primary-color digital-graphic-encoding polarization modulator are adapted collectively to reflectively spatially modulate on a pixel array basis the polarization of a linearly polarized component-primary-color dark-pixel-polarization-state output subbeam projected from the corresponding component-primary-color subbeam output/input optical port of the beam color dividing/combining optics onto the polarization-modulator face in accordance with a corresponding primary-color component graphic of a desired composite color digital graphic to form a reflected mixed-polarization graphics-encoded component-primary-color input subbeam directed into the corresponding component-primary-color subbeam output/input optical port. Preferably, the graphics display image plane has an array of composite-color pixel locations defined with respect thereto. Each such composite-color pixel location in the graphics display image plane preferably corresponds to three reflective polarization-modulator pixel elements located respectively at effectively congruent positions on the polarization-modulator faces of the three reflective component-primary-color polarization modulators.
Preferably, a composite-color image test-point location is defined in the graphics display image plane of a projection display of the invention laterally displaced from the intersection of the projection-optics central axis with the graphics display image plane. Such image test-point location preferably corresponds to a location of a single composite-color pixel in the graphics display image plane. The composite-color image test-point location in the graphics display image plane preferably corresponds to three reflective polarization-modulator object test-point pixel elements located respectively at effectively congruent positions on the polarization-modulator faces of the three reflective component-primary-color polarization modulators, laterally displaced from the respective polarization-modulator-face central-axis intersection points of the polarization-modulator faces. Preferably, for each component primary color, a component-primary-color test-point chief ray trace is defined, tracing as a ray of light-pixel-polarization-state linearly polarized light of the component primary color, from the composite-color image test-point location in the graphics display image plane through the projection optics passing through a center point of the projection-optics aperture stop, through the polarizing beamsplitter, and through the beam color dividing/combining optics to intersect the polarization-modulator face of the corresponding component-primary-color polarization modulator at a point laterally displaced from the polarization-modulator-face central-axis intersection point of the polarization-modulator face. Each of the three component-primary-color test-point chief ray traces follows a component-primary-color-dependent path manifesting chromatic aberrations of the optics through which the chief ray trace passes including the lateral-color chromatic aberration. The projection-optics aperture-stop location of the projection-optics aperture stop is a nontelecentric aperture-stop location such that each component-primary-color test-point chief ray trace intersects the polarization-modulator face of the corresponding component-primary-color polarization modulator at a nontelecentric angle of intersection inclined with respect to a normal to the modulator face at the point of intersection. Each of the three reflective component-primary-color polarization modulators is individually positioned axially along the corresponding component-primary-color subbeam output/input central axis of the corresponding component-primary-color subbeam output/input optical port of the beam color dividing/combining optics so that, taking into account the nontelecentric angle of intersection of the component-primary-color test-point chief ray trace with the polarization-modulator face of the corresponding component-primary-color polarization modulator and chromatic aberrations of the optics through which the chief ray trace passes including the lateral-color chromatic-aberration differences in lateral magnification at the respective component primary colors, the corresponding component-primary-color test-point chief ray trace intersects the polarization-modulator face of the corresponding component-primary-color polarization modulator effectively at the polarization-modulator object test-point pixel element. Preferably, the respective polarization-modulator-face axial-position distances of the polarization-modulator faces of at least two of the three reflective component-primary-color digital-graphic-encoding polarization modulators of the projection display of the invention differ from one another so that differences in the lateral magnification of light rays of different component primary colors caused by the lateral-color chromatic aberration of the projection optics tend to be compensated for over the composite-color graphics imaged by the projection optics in the graphics display image plane.
Preferably, the component primary colors of a projection display of the invention are red, green and blue.
The composite-color image test-point location is preferably located in the periphery of the graphic display image plane of a projection display of the invention. Preferably, the composite-color image test-point location is located on the perimeter of the graphic display image plane.
Preferably, the respective polarization-modulator-face axial-position distances of the polarization-modulator faces of the three reflective component-primary-color digital-graphic-encoding polarization modulators differ from one another in a projection display of the invention.
Preferably, the polarization-modulator face of each reflective component-primary-color polarization modulator of a projection display of the invention is located at least proximate to a corresponding component-primary-color object plane optically conjugate to the graphics display image plane. One or more of the polarization-modulator faces may be spaced apart from the corresponding component-primary-color object plane a component-primary-color pixel-convergence defocus distance so that the corresponding component-primary-color test-point chief ray trace intersects the polarization-modulator face effectively at the polarization-modulator object test-point pixel element.
Suitable polarizing beamsplitters for the projection display of the invention include MacNeille-type multilayer dielectric film polarizing beamsplitters, wire-grid-polarizer polarizing beamsplitters, or alternating birefringent/nonbirefringent-film-polarizer polarizing beamsplitters. MacNeille-type multilayer dielectric film polarizing beamsplitters are described generally in U.S. Pat. No. 2,403,731 to MacNeille and U.S. Pat. No. 5,453,859 to Sannohe and Miyatake. Wire-grid-polarizer polarizing beamsplitters are generally described in published International PCT patent applications No. WO 01/09677 and No. WO 00/70386. Alternating birefringent/nonbirefringent-film-polarizer polarizing beamsplitters are described generally in published International PCT patent application No. WO 00/70386.
Beam color dividing/combining optics for a projection display of the invention preferably includes assemblies of prisms with dichroic mirrors mounted on faces of the prisms and assemblies of plate-mounted dichroic mirrors.
The projection optics of projection displays of the invention preferably deviate only modestly from a telecentric condition. Deviating from a telecentric condition in the projection optics; that is, using a finite pupil instead of an infinite pupil; establishes an angled geometry for gathering light off axis for projection by the projection optics. The angled geometry for off-axis light gathering may be used to compensate for lateral color.
A finite pupil position also helps the design of the projection optics in general. Placing the pupil closer to the physical lens assembly is a simpler constraint than the infinite pupil location of a telecentric lens assembly. Providing latitude in specifying the nontelecentric pupil location of projection optics represents a design freedom which tends to simplify the design of projection optics of projection displays of the invention relative to the design of comparable telecentric projection optics. The telecentric condition does help for uniformity of image and angular acceptance of the prism color splitting and polarization splitting components. Thus, the deviation from the telecentric condition is preferably kept modest or small for projection optics of projection displays of the invention.
Providing a separate object plane for each of the three primary colors provides a design freedom which tends to simplify the design of projection optics of projection displays of the invention relative to requiring a single object plane for the three primary colors.
A small amount of defocus may be used to shift the lateral offset of component-color object graphics to adjust color convergence in projection displays of the invention.